For example, in a projector for image display such as a DLP™ projector and a liquid crystal projector, a photomask exposure apparatus, etc., a high intensity discharge lamp (an HID lamp) such as a xenon lamp and a super-high pressure mercury lamp has been used. A principle diagram of an example of such a projector is illustrated in FIG. 15 (reference: Japanese Unexamined Patent Application Publication No. 2004-252112, etc.).
In a projector illustrated in FIG. 15, light derived from a light source (SjA) configured of a high intensity discharge lamp or the like is inputted into an incident end (PmiA) of a light uniformizing section (FmA) via a light condensing section (illustration thereof is omitted) configured of a concave reflector, a lens, etc., and is outputted from an emission end (PmoA) thereof. Here, for example, an optical guide may be used as the light uniformizing section (FmA). The optical guide is also called by a name such as a rod integrator or a light tunnel, and may be configured of a rectangular cylinder made of a light transmissive material such as glass or resin. Light inputted into the incident end (PmiA) propagates inside the light uniformizing section (FmA) while being totally reflected by side faces of the light uniformizing section (FmA) repeatedly on the basis of a principle same as that of an optical fiber. This achieves a function of sufficiently uniformizing illuminance on the emission end (PmoA) even when distribution of the light inputted into the incident end (PmiA) is non-uniform.
It is to be noted that, other than that described above that is configured of the rectangular cylinder made of the light transmissive material such as glass or resin, the optical guide mentioned above may be an optical guide configured of a hollow square tube that has inner faces configured of reflectors and causes light to propagate therein while being reflected repeatedly by the inner faces in a similar manner, which thereby achieves a similar function.
An illumination lens (Ej1A) is disposed at a position to face the emission end (PmoA) so that an image of a quadrangle at the emission end (PmoA) is formed on a two-dimensional light amplitude modulation device (DmjA). The two-dimensional light amplitude modulation device (DmjA) is thereby illuminated with the light outputted from the emission end (PmoA). It is to be noted that, in FIG. 15, a mirror (MjA) is disposed between the illumination lens (Ej1A) and the two-dimensional light amplitude modulation device (DmjA).
Further, in accordance with an image signal, the two-dimensional light amplitude modulation device (DmjA) modulates, for each pixel, the light and thereby causes the light to travel in a direction guided to a projection lens (Ej2A), or causes the light to travel in the direction not guided thereto. As a result, an image is displayed on a screen (Tj).
Incidentally, a two-dimensional light amplitude modulation device as that described above may be called a light bulb in some cases. In the case of the optical system illustrated in FIG. 15, a DMD™ (a digital micro-mirror device) is generally used as the two-dimensional light amplitude modulation device (DmjA).
The light uniformizing section may also be that called a fly eye integrator, other than the optical guide described above. A principle diagram of an example of a projector that uses such a light uniformizing section is illustrated in FIG. 16 (reference: Japanese Unexamined Patent Application Publication No. 2001-142141, etc.).
In the projector illustrated in FIG. 16, light derived from a light source (SjB) is inputted, as a substantially-parallel bundle of rays, to an incident end (PmiB) of a light uniformizing section (FmB) configured of a fly eye integrator via a collimator section (illustration thereof is omitted), and is outputted from an emission end (PmoB) of the light uniformizing section (FmB). The light source (SjB) may be configured of a high intensity discharge lamp or the like, and the collimator section may be configured of a concave reflector, a lens, or the like. Here, the light uniformizing section (FmB) is configured of a combination of an upstream fly eye lens (F1B) disposed on the incident side, a downstream fly eye lens (F2B) disposed on the emission side, and an illumination lens (Ej1B). Both of the upstream fly eye lens (F1B) and the downstream fly eye lens (F2B) are formed of a number of quadrangular lenses that have the same focal length and the same shape and are arranged in a matrix.
Each of the lenses in the upstream fly eye lens (F1B) and a corresponding lens in the downstream fly eye lens (F2B) configure an optical system called a Köhler illumination, which means that a number of Köhler illumination optical systems are arranged in a matrix. The Köhler illumination optical system is generally configured of two lenses. In this Köhler illumination system, when the upstream lens condenses light to illuminate a targeted plane, the upstream lens does not form an image of the light source on the targeted plane, but forms the image of the light source on a surface in the center of the downstream lens. Further, the downstream lens is so arranged as to cause an image of a quadrangle of an outer shape of the upstream lens to be formed on a targeted plane (a plane to be illuminated), and the targeted plane is thereby illuminated uniformly. If the downstream lens is not provided, when the light source is not a complete point light source and has a finite size, illuminance of a peripheral portion of the quadrangular targeted plane is degraded depending on the size. A function of the downstream lens is to prevent such a phenomenon. Accordingly, uniform illuminance is achieved, due to the downstream lens, even in the peripheral portion of the quadrangular targeted plane independently of the size of the light source.
Here, in the case of the optical system illustrated in FIG. 16, because it is considered a basis that a substantially-parallel bundle of rays is inputted to the light uniformizing section (FmB), the upstream fly eye lens (F1B) and the downstream fly eye lens (F2B) are so arranged that a spacing therebetween is equal to a focal length thereof. Consequently, an image of a targeted plane of a uniform illumination as the Köhler illumination optical system is generated at the infinite. However, the illumination lens (Ej1B) is disposed downstream of the downstream fly eye lens (F2B). This brings the targeted plane from the infinite onto a focal surface of the illumination lens (Ej1B). A number of Köhler illumination optical systems arranged in a matrix are parallel to an incident optical axis (ZiB) and a bundle of rays is inputted substantially axisymmetrically to a central axis of each of the Köhler illumination optical systems. Because a bundle of output rays is also substantially axisymmetrical, the rays incident on a lens surface at the same angle are refracted toward the same point on the focal surface, independently of an incident position on the lens surface. Due to such properties of the lens, i.e., the Fourier transform function of the lens, all of outputs from the Köhler illumination optical systems are formed into images on the same targeted plane on the focal surface of the illumination lens (Ej1B).
As a result, all of the illumination distributions of the respective lens surfaces in the upstream fly eye lens (F1B) are overlapped with one another. Accordingly, there is formed on the incident optical axis (ZiB) a single image, of synthesized quadrangles, that has illumination distribution more uniform than that in a case where a single Köhler illumination optical system is provided.
By disposing the two-dimensional light amplitude modulation device (DmjB) at a position of the image of the synthesized quadrangles, the two-dimensional light amplitude modulation device (DmjB) which is a target of illumination is illuminated with the light outputted from the emission end (PmoB). It is to be noted that, upon illumination, a polarization beam splitter (MjB) is disposed between the illumination lens (Ej1B) and the two-dimensional light amplitude modulation device (DmjB) to thereby allow the light to be reflected toward the two-dimensional light amplitude modulation device (DmjB).
Further, in accordance with an image signal, the two-dimensional light amplitude modulation device (DmjB) modulates and reflects, for each pixel, the light so as to rotate a polarization direction of the light by 90 degrees or so as not to rotate the polarization direction of the light. Thus, only the rotated light passes through the polarization beam splitter (MjB) to be incident on a projection lens (Ej3B), and an image is displayed on the screen (Tj) accordingly.
It is to be noted that, in the case of the optical system illustrated in FIG. 16, LCOS™ (a silicon liquid crystal device) is generally used as the two-dimensional light amplitude modulation device (DmjA). In a case of such a liquid crystal device, only a component of light that has a specified polarization direction is allowed to be modulated effectively. For this reason, a polarized-light alignment functional device (PcB) may be typically inserted, for example, downstream of the downstream fly eye lens (F2B). The polarized-light alignment functional device (PcB) is for allowing a component parallel to the specified polarization direction to pass therethrough as it is but rotating a polarization direction of a component perpendicular to the specified polarization direction by 90 degrees, and thereby allowing all of the light to be utilized efficiently.
Also, a field lens (Ej2B) may be inserted, for example, immediately upstream of the two-dimensional light amplitude modulation device (DmjB) so that substantially-parallel light is incident on the two-dimensional light amplitude modulation device (DmjB).
It is to be noted that, as the two-dimensional light amplitude modulation device, a transmissive liquid crystal device (LCD) may also be used in an optical arrangement appropriate therefor, other than a reflective device as that illustrated in FIG. 16 (reference: Japanese Unexamined Patent Application Publication No. H10-133303, etc.).
Incidentally, the following measures have been taken in a typical projector to display a color image. Specifically, for example, a dynamic color filter such as a color wheel may be arranged downstream of the light uniformizing section to illuminate the two-dimensional light amplitude modulation device with a bundle of color-sequential rays of R, G, and B (red, green, and blue), which achieves color display in a time-divisional manner. Alternatively, a dichroic mirror, a dichroic prism, or the like may be disposed downstream of the light uniformizing section to illuminate, with light separated into three primary colors of R, G, and B, the two-dimensional light amplitude modulation devices provided independently for the respective colors, and a dichroic mirror, a dichroic prism, or the like may be disposed for performing color synthesis on the bundle of modulated rays of the three primary colors of R, G, and B. It is to be noted that a dichroic mirror, a dichroic prism, or the like is omitted in FIGS. 15 and 16 to avoid complicated illustration.
However, the high intensity discharge lamp described above has had disadvantages such as low efficiency in conversion from supplied electric power into optical power, i.e., a large heat loss, or a short life. As an alternate light source that has overcome these disadvantages, a solid-state light source such as an LED and a semiconductor laser has been attracted attention recently. Out of these, the LED has smaller heat loss and a longer life, compared to the discharge lamp. However, light emitted by the LED has no directivity as with the light emitted by the discharged lamp. This causes an issue of low efficiency in utilizing light in an application in which only light in a particular direction is utilizable, for example, in the projector, the exposure apparatus, or the like described above.
On the other hand, the semiconductor laser has a small heat loss and a long life as with the LED, and has high directivity in addition thereto. Accordingly, the semiconductor laser has an advantage of high efficiency in utilizing light also in the application in which only light in a particular direction is utilizable, for example, in the projector, the exposure apparatus, or the like described above. However, on the other hand, the semiconductor laser has an issue that a speckle occurs.
Here, a speckle is a spotty or patchy pattern that inevitably appears when coherent light is projected. The coherent light may be light of a semiconductor laser, light of any other laser, or light generated, for example, by performing wavelength conversion on laser light (by utilizing non-linear optical phenomenon such as harmonic generation or optical parametric effect). The speckle is an extremely-unwanted phenomenon that largely degrades image quality in application of generating an image to be viewed, for example, the above-described projector, or in an application of precisely exposing a coating film made of a photosensitive material to have a pattern of a photomask. For this reason, many measures have been proposed for a long time for improvement thereof.
For example, Patent Literature 1 describes a laser display apparatus that rotates a fly eye integrator, and thereby rotates, around an optical axis serving as a rotation axis, an angle of light applied onto a two-dimensional light amplitude modulation device.